In fine processing for manufacturing a device such as a semiconductor device or a Flat Panel Display(FPD), plasma processing is performed on a workpiece such as a semiconductor substrate or a glass substrate. In the plasma processing, control with respect to a temperature or a temperature distribution of the workpiece in addition to control with respect to a plasma density distribution on the workpiece is important. If the temperature control with respect to the workpiece is not appropriately performed, uniformity of reaction in the surface of the workpiece cannot be secured, and manufacturing yield of the device deteriorates.
In general, in a plasma processing apparatus which is used in plasma processing, a mounting table on which a workpiece is placed is provided in a processing container. The mounting table has a high-frequency electrode function which applies high frequency wave to a plasma generation space, a holding function which holds a workpiece by electrostatic attraction or the like, and a temperature control function which controls the temperature of a workpiece by heat transfer.
In the plasma processing which uses such a plasma processing apparatus, a distribution in heat input characteristics with respect to the workpiece may be occur due to nonuniformity of plasma and radiant heat from a wall configuring the processing container, and/or a heat distribution in the mounting table. Accordingly, it is necessary to appropriately correct the heat distribution of the workpiece with the temperature control function of the mounting table.
Conventionally, a heater, which is a resistive heating element, is incorporated into the mounting table as the temperature control function in order to control the temperature of the mounting table and the temperature of the workpiece. The temperature of the workpiece is controlled by controlling a current supplied to the heater. As described above, the heat input characteristics with respect to the workpiece have a nonuniform distribution. Accordingly, in order to eliminate the nonuniform heat input characteristics, a mounting table has been developed which is configured by providing a plurality of heaters in a plurality of segments defined in the mounting table, respectively. Moreover, it is necessary to set regions of a workpiece which are temperature control objects into finely divided regions according to a process, and therefore, as described in Patent Literature 1, it is necessary to increase the number of the segments defined in the mounting table.
In order to individually control the temperatures of the plurality of regions of the workpiece by the plurality of heaters provided in the mounting table as described above, it is necessary to appropriately control electric power supplied to the heaters. To this end, in general, a thyristor which adjusts the electric power supplied to each heater is provided between each heater and a power source, as described in Patent Literature 2. FIGS. 8A and 8B are diagrams illustrating a principle of a thyristor. In general, the thyristor adopts a phase control method, and as shown in FIG. 8A, it is possible to control a period within which the heater and the power source are electrically connected to each other, that is, a conduction angle θ, by performing switching between ON/OFF. Accordingly, a current shown in FIG. 8B is supplied to the heater.